The present invention relates to passive infrared intrusion detectors, and particularly to such detectors which are arranged for mounting to the ceiling of a room or other space to be protected.
U.S. Pat. No. 4,275,303, which is assigned to the same assignee as the present invention, describes a passive infrared intrusion detector which includes an enclosure having an aperture with a multi-segment Fresnel lens which is provided for focusing infrared energy onto a sensing element within the enclosure. As described in the referenced patent, there is provided a light source within the enclosure which provides for locating the orientation of the beams of infrared sensitivity of the device by observation of emitted light from the detector. The device described in the referenced patent, and many other prior art passive infrared intrusion detectors, are arranged for mounting to the wall of a room to be protected so that the beams of infrared sensitivity radiate outward from the wall, often in multiple directions.
It is an object of the present invention to provide a new and improved passive infrared intrusion detector which is arranged for mounting to the ceiling of a room to be protected, whereby beams of infrared sensitivity can radiate in many directions and reach areas throughout the room, which might be otherwise blocked from observation by a single wall mounted detector. It is a further object of the invention to provide such a detector which includes a dual element detector and a light emitting element within the detector for purposes of locating the orientation of the beams of infrared sensitivity.